Pancreatic islet transplantation (PIT) is an attractive treatment for patients with type I diabetes (IDDM). However, there are major obstacles to overcome before PIT can become a routine therapeutic procedure. One is the need for chronic immunosuppression and the other is the shortage of cadaveric organs. In respect of the former, we have demonstrated islet allografts tolerance without maintenance immunosuppressive drug therapy in unrelated diabetic primates. With respect to the shortage of human pancreatic tissue, pigs are an attractive source of islets because they breed rapidly, a long history of porcine insulin in humans, and the potential for genetic engineering. Unfortunately, exposure of porcine islets to fresh human or primate serum resulted in acute islet damage mainly mediated by xenoreactive natural antibodies (XNA) and complement (C). Under certain circumstances, when XNA and C-mediated immune responses are inhibited for a few days, grafts can survive indefinitely despite the return of XNA and C, a phenomenon referred as "accommodation". Expression in the graft of anti-apoptotic or "protective genes", such as Bcl-2, A20 BcI-xL and heme oxygenase-1 (HO-1), make the graft resistant to rejection. The long-range goal of this project is to develop an effective and practical treatment to reverse human IDDM. To accomplish this goal, we will establish in diabetic primates, a strategy for islet cytoprotection and tolerance induction to isolated adult porcine pancreatic islets. Our approach combines genetic modification of porcine islets to overexpress Bcl-2 and a brief immunosuppressive treatment based on peritransplant administration of anti-CD3-Immunotoxin (IT) and 15-Deoxyspergualin (DSG), a combination that builds upon our previous studies of tolerance induction to kidney, islets and skin allografts in primates. In addition, our laboratory recently documented the ability to cryoprotect in vitro porcine islets against the cytotoxic effects of primate XNA and C through genetic modification of porcine islets to overexpress Bcl-2. Furthermore, we have demonstrated the ability of this gene to prevent loss of functional islet mass after transplantation. With these considerations in mind, we hypothesize that cytoprotection of porcine islets by ex vivo gene transfer of Bcl-2 gene will facilitate long-term survival following transplantation into diabetic primate recipients treated with the standard IT plus DSG tolerance induction protocol. Our Specific Aims are: 1) To evaluate the survival of genetically modified adult porcine pancreatic islets to overexpress Bcl-2 in streptozotocin-induced diabetic primates treated with a tolerance induction protocol based on IT and DSG, and 2) To examine the metabolic capacity of genetically modified xeno-islets transplanted into diabetic primates in the absence of chronic immunosuppressive drugs. The research proposed in this grant will provide significant information to the xenotransplant research and the potential use of porcine islets as an alternative to human tissue for pancreatic islet transplantation.